Conventionally, an endoscope apparatus that irradiates illumination light to obtain an endoscopic image inside a body cavity is widely used as a biological observation apparatus. An endoscope apparatus of this type uses an electronic endoscope having image pickup means that guides illumination light from a light source into a body cavity using a light guide or the like and which picks up a subject image from returning light thereof, and is arranged so that signal processing of an image pickup signal from the image pickup means is performed by a video processor in order to display an endoscopic image on an observation monitor for observing an observed region such as a diseased part.
One method of performing normal biological tissue observation using an endoscope apparatus involves emitting white light in the visible light range from a light source, irradiating frame sequential light on a subject via a rotary filter such as an RGB rotary filter, and obtaining a color image by performing synchronization and image processing on returning light of the frame sequential light by a video processor. In addition, another method of performing normal biological tissue observation using an endoscope apparatus involves positioning a color chip on a front face of an image pickup plane of image pickup means of an endoscope, emitting white light in the visible light range from a light source, picking up images by separating returning light of the frame sequential light at the color chip into each color component, and obtaining a color image by performing image processing by a video processor.
With biological tissue, absorption characteristics and scattering characteristics of light differ according to the wavelength of irradiated light. For example, Japanese Patent Laid-Open 2002-95635 proposes a narrowband light endoscope apparatus that irradiates illumination light in the visible light range on biological tissue as narrowband RGB frame sequential light having discrete spectral characteristics to obtain tissue information on a desired deep portion of the biological tissue.
In addition, Japanese Patent Laid-Open 2003-93336 proposes a narrowband light endoscope apparatus that performs signal processing on an image signal obtained from illumination light in the visible light range to create a discrete spectral image and to obtain tissue information on a desired deep portion of the biological tissue.
With the apparatus described in the above-mentioned Japanese Patent Laid-Open 2003-93336, processing for creating a spectral image signal such as that obtained when using a narrow bandpass filter is performed through electrical arithmetic processing by matrix computation (corresponding to a quasi-narrow bandpass filter) on a color image signal (also referred to as a living body signal) picked up in the broadband wavelength range without using an optical narrow bandpass filter.
However, the apparatus described in the above-mentioned Japanese Patent Laid-Open 2003-93336 has disadvantages including declines in the accuracy of a created spectral image signal, such as a difference in spectral reflection characteristics caused by a difference in biological tissue to be observed creates perturbations in the created spectral image.
For example, in a case where the observation object is the esophagus mucosa or the gastric or large intestinal mucosa, the difference in the type of mucosal tissue (for example, esophagus mucosa is stratified squamous epithelia while gastric mucosa is simple columnar epithelia) gives rise to disadvantages such as a difference in spectral reflection characteristics caused by a difference in mucosal tissue.
In addition, the apparatus described in the above-mentioned Japanese Patent Laid-Open 2003-93336 has a disadvantage in that color tones during output/display of a spectral image signal on display means or a display output device cannot be changed.
As seen, while the apparatus described in the above-mentioned Japanese Patent Laid-Open 2003-93336 has an advantage in that a spectral image signal can be electrically created from a color image signal, it is desired that interface means or the like capable of further enhancing operability is provided, such as converting and displaying a spectral image signal in a color tone desired by a user or an appropriate color tone, or switching and displaying a color image signal (normal image signal) and a color image signal.
Furthermore, the apparatus described in the above-mentioned Japanese Patent Laid-Open 2003-93336 simply outputs an obtained spectral image to a monitor. Therefore, with the apparatus described in the above-mentioned Japanese Patent Laid-Open 2003-93336, not only is there a risk in that an image displayed on the monitor may not be an image having color tones suitable for the observation of issue information in a desired deep portion of biological tissue, it becomes difficult to grasp the relationship to living body function information held by a living body such as the hemoglobin content of blood.
The present invention is made in consideration of the above, and an object thereof is to provide a biological observation apparatus having a function for electrically creating a spectral image signal from a color image signal which is also capable of creating a spectral image signal that can appropriately accommodate differences among biological tissue and the like and improving operability related to spectral image observation and the like.
Another object of the present invention is to provide a biological observation apparatus capable of calculating living body function information related to the blood of a living body based on a spectral image signal obtained through signal processing, thereby contributing towards the improvement of diagnostic performance.